Although no beach in Cornwall is a complete secret, there is no shortage of inaccessible bays, without car parks, cafes and many of these are perfect for rock pooling. The extra effort of walking (in my case sliding) down a steep field and hauling back up it at the end of the day pays off. This secret beach, one of several between Falmouth and the Helford river is a complete gem, just as diverse as I remember it.

Cornish Rock Pools Junior’s friends who appeared on Countryfile with us have joined us today. Unlike Portreath, the north coast beach we filmed at, it’s incredibly easy to find creatures on this sheltered shore.

Our first discovery is that a population of St Piran’s hermit crabs has established here, probably new since my last visit several years back. I spot the tell-tale red antennae poking out of a shell.

St Piran’s hermit crabs reappeared in Cornwall a few years ago after a long absence. The red antennae and chequerboard eyes make them instantly recognisable.

We haven’t gone far before we come across a lovely long pool with plenty of loose boulders to provide protection to sea creatures. As I turn a rock, Junior spots a large fish that shoots out and noses into a clump of seaweed at the edge of the pool to hide. I put Other Half on the case. He skillfully coaxes it into a corner of the pool in the hope it will swim into his big bucket, which it obligingly does.

The underside of the rock I’ve turned is crowded with life. There are colourful patches of sponges and sea squirts. A clutch of yellow eggs coats part of the surface.

Close up of Cornish clingfish (Lepadogaster purpurea) eggs showing the eyes and spotty tails

These are clingfish eggs and the parent will be nearby. Within them, the babies are developing fast. A pair of eyes gazes out of each egg and the tails, wrapped tightly round the little heads are visible too. Something close by catches my attention, a colourful slug.

Calma glaucoides sea slug

The slug’s long, yellow-tipped cerata sway like hair in the current, giving it a puffed-up appearance. It’s an attractive animal, a pale blue colour when it catches the light. This slug, Calma glaucoides, specialises in eating fish eggs, and especially likes those of the clingfish.

Meanwhile, Other Half and Junior are excited about the fish in their bucket. Junior reckons it’s a giant goby and I think he may be right. I try to pick it up to try to confirm the species by taking a look at the fin under its belly, but the fish is very lively.

Giant goby

Junior deploys his best trout tickling skills to persuade the fish to lie still in his hands, which it eventually more or less does. The sucker-fin underneath has a thick, pointed lobe at the front.

The fleshy sucker fin underneath the giant goby has a point at the front – but the fish isn’t keen on staying still for me to get a better photo.

The fish has the small eyes and the salt-and-pepper colouring typical of a giant goby and lacks the yellow band on the top of the first dorsal fin which identified the more common rock goby. Its fins are tipped with grey instead. This fish is highly protected and it’s important not to disturb or trap them without a licence, so, Junior carefully lowers the bucket into the pool allowing his goby friend to swim straight back to its favourite hiding place.

Other finds come in so fast, it’s hard to keep up with them. We come close to catching a huge mystery fish, which thrashes through the seaweed but escapes without being seen. I find a small yellow slug which I initially assume is Jorunna tomentosa, which I often see on the shore. It’s only when I look at the photos at home that I realise my mistake. This slug has lumpy protrusions all over its body that have a sandy, almost warty appearance.

Doris ocelligera – a species I’ve never seen before, but which seems to be having a good year in southern UK and northern France.

I’ve never seen anything like it, the reason being that this slug has only rarely been recorded in the UK. Doris ocelligera tends to occur further south but seems to be becoming more established in the south of the UK and northern France, with several records coming in over the last few weeks. An exciting find and one I’ll have to look out for more carefully in future.

Thanks go to David Fenwick of Aphotomarine for confirming this slug’s identity.

Doris ocelligera

One of Louis’s friends finds this fabulous spider crab.

It’s hard to tell that this is a spider crab and not a lump of seaweed!

It’s a female which has decorated herself in so much seaweed that, unless she moves, it’s impossible to tell she’s not just another rock. We have a good look at her amazing stalked eyes and spiny shell before returning her safely into the seaweed.

Spider crab

The children’s mums aren’t to be outdone. They get stuck in and bring me all sorts of lovely things. This Ophiothrix fragilis common brittle star has a wonderful bright orange centre.

Brittle star with a lovely orange central disk – Ophiothrix fragilis

Another mum finds brilliant yellow Berthella plumula slugs, paired together under a stone ready to spawn.

Berthella plumula sea slugs

This white-ruffed sea slug (Aeolidella alderi) was another lovely find.

Aeolidella alderi – the white-ruffed sea slug

The rocks of the lower shore are covered in all sorts of colourful wildlife. Ciona intestinalis sea squirts tipped with bright yellow rings, blue star ascidian sea squirts and lots of variegated scallops decked out in marbled patterns of brilliant orange and pink.

Ciona intestinalis sea squirt

One variegated scallop opens its shell and swims away in jerking side to side movements, like a leaf falling from a tree.

A variegated scallop prepares to swim away

Before we know it, the tide is pushing in and we slip and slide our way across the seaweed-covered rocks back to the sand. The time between the tides is short, just enough to give us a glimpse into this extraordinary marine community before the sea rolls in to cover everything once more. We sit and watch oystercatchers, herons and even a pair of swans fly across the sea, while the children set off into the distance with a metal detector, onto new adventures already.

Visiting a beach like this is an extraordinary privilege. We make sure to leave everything unharmed, to pick up any litter we see and to leave nothing behind. I’m already looking forward to my next visit.

The sun breaks through the cloud as the first children arrive. It’s a perfect day for a Wildlife Watch expedition and although I don’t know the beach at Coverack well, a quick paddle in the rippling shallows has already yielded sand eels, an attractive pink thin tellin shell and plenty of shore crabs so it’s shaping up well.

Lesser sand eel – being dark on top and light underneath makes it harder for predators to spot them in the water.

I always look forward to meeting my Wildlife Watch groups and this one doesn’t disappoint. My assistant, Vicky, does a fabulous job of welcoming everyone and helping set up and the children are enthusiastic and curious, raring to get stuck in. It’s especially good to see how well the kids care for the animals, making sure they have enough water in their tubs, replacing any stones and seaweed they move and not detaching animals that might get damaged like anemones and limpets.

One lad is particularly adventurous and knowledgeable, so we have fun investigating a gully between two huge rocks. We find the inner face of one rock is covered in a massive sheet of breadcrumb sponge and there are especially large strawberry anemones in the pool beneath. My new friend stays there trying to catch an elusive fish while I help others identify creatures.

Soon, the finds are coming in to our makeshift shore laboratory. Glittering sand eels, a feisty velvet swimming crab with devilish red eyes, a whole troop of hermit crabs and colourful brittle stars which we watch walking on their long arms.

My new friend comes over with a shore crab. He’s learned that they keep their eggs under their tails and is excited to find one he thinks is in berry. He seems disappointed when I reveal that, although she has something under there, it’s not eggs. But this is something far more exciting. It’s a parasitic barnacle, Sacculina carcini, which I’ve been searching for and never seen. The yellow mass under the crab’s tail is the barnacle’s fruiting body, the barnacle’s eggs – not the crab’s.

This green shore crab has a yellow lump under her tail – the parasitic barnacle Sacculina carcini

Unfortunately for the crab, once it is infected it can no longer moult and grow or lay eggs. The barnacle will take a lot of energy from the crab as it spreads through its body. It can even trick male crabs into behaving like females to ensure that they will successfully release the barnacle’s young when the eggs are ready to hatch. It’s amazing to see, even if it’s not good news for the crab.

The yellow lump under the tail contains the eggs of the parasitic barnacle which has infested the crab.

As always, I get more than a little distracted doing my own rock pooling. I can’t help myself. I briefly feel guilty that I’m not available enough to the children while I’m crawling about among the slippery boulders, but then I spot a miniscule thing moving on the rock and it has my entire attention.

The thing looks like a tiny lobster. I scramble to grab a suitable pot and when I look back at the rock I can’t see it any more. I stare at the area where I saw it but it’s just not there. I look all around the surface of the rock in vain, gently tip a little sea water down it to see if anything moves but I’m scared I might wash it off accidentally.

When I finally relocate my mini crustacean, it is nearly at the edge. With a lot of care and determination, I succeed in catching it in my pot. It’s only about 5mm long, but seems to be a tiny squat lobster, the smallest I’ve ever seen.

Tiny squat lobster about 5mm long (Galathea sp.) at Coverack, Lizard

Back at the trays, we all gather round to take a close look at all the animals and learn about their lives and strange habits. We have a fabulous diversity of creatures to watch before they’re returned to the shore.

I slip my baby squat lobster into a petri dish to take some photos. It looks a bit strange, as though something has got caught on its back legs. When I look a couple of minutes later, the thing that’s stuck to it has grown. It’s hard to see as the whole animal is only a few millimetres long, but when the ‘thing’ comes away I’m in no doubt. The squat lobster is growing and has just shed its old skin.

Moult of the squat lobster – the animal has moved out of its old shell so that it can grow.

The old carapace is an exact replica of the animal, only colourless and transparent. As the new, soft shell of the squat lobster begins to harden it seems to grow before our eyes.

A day at Kynance Cove on the Lizard Peninsula has become a fixture in the Cornish Rock Pools calendar. The smooth, serpentine cliffs don’t create many hiding places for marine life, but Junior loves the geology and caves. There are always creatures to see too if you look carefully enough, so I take the opportunity to relax in the sun, staring at fish through the clear water.

The funny thing is that, while I stare in, the fish stare back, creeping closer up the sides, over pink encrusting algae and through fronds of the Corallina seaweed to secure a better view. Bold young shannies, prop themselves up on their two-pronged pectoral fins, swivelling their colourful clown eyes to observe me.

Being watched… a young shanny (common blenny) edges up the side of the pool to take a look at me. Kynance Cove, Lizard, Cornwall.

In the far corner of the pool, a Montagu’s blenny pops up to say hello. It’s easily recognisable by its pronged head tentacle, which looks like a tiny Christmas tree.

The Montagu’s blenny almost gets out of the water to take a look at me. Kynance Cove, Cornwall.

The surrounding rocks are covered in barnacles, which suits these fish well. The Montagu’s blenny likes nothing better than to nibble the feeding legs off barnacles.

I soon start to doubt that this fish is just curious. Unlike the shannies, which are just juveniles, this Montagu’s blenny is full size and sports a fine pattern of turquoise spots on his body. It is the male blenny’s job to guard the eggs, and this fish is taking no prisoners.

This bold Montagu’s blenny has striking blue spots and a dark stripe through its eye.

He seems determined to chase me out of his territory, repeatedly headbutting my camera. He may only be 7cm long, but I have a feeling that if I put a finger in the water he won’t hesitate to take me on with his sharp little teeth.

Blennies’ thick lips make them look like they’re smiling, but this Montagu’s blenny just wants to attack my camera!

The hard rock becomes uncomfortable to lie on after a while, digging into my legs, but I try not to change position. The fish will scatter if I make any sudden movement or noise. Half a dozen shannies are darting around the bottom of the pool, while others are basking in shallow grooves at the edge. The Montagu’s blenny doesn’t take his eye off my camera.

I watch him until the tide turns and the waves begin to sweep in. This may not be the most diverse rock pooling beach, but the fish are a joy to watch and it’s a wonderful spot to while away a sunny morning before enjoying a pasty in the café. Summer starts here!

I should be at home, cracking on with some work, but I’ve heard there are comb jellies about and I could do with some photos for my jellyfish course for ERCCIS.

Any excuse.

I cut through overgrown vegetation, down the cliff path to a favourite cove. In the ten minutes it’s taken me to walk here, the grey clouds have lifted and the sea’s looking good enough to dive into.

My progress through the rocky gully is slow. The warm weather has brought an explosion of slippery sea lettuce which blocks my view of my feet as they feel for underwater rocks. Tangles of pink spaghetti, the eggs of sea hares, are wrapped around many of the green fronds and a close inspection reveals that dozens of stalked jellyfish (Haliclystus octoradiatus) have already made their homes here.

As I move into deeper water, something catches my eye, floating below the surface. It’s so transparent it’s barely there, but it shimmers intermittently. With some difficulty, the current swishing the jelly back and forth, I scoop it up and carry it in cupped hands to a sheltered overhang. For a moment I think I’ve dropped it, then it swims out.

Barely there – a transparent Beroe cucumis comb jelly in my hand

I’m treated to a fabulous display of iridescence as the comb jelly beats its tiny combs, sending a trail of light and colour up the lines on its tiny body.

Between the current washing into the pool and the jelly’s own surprisingly speedy swimming efforts, it slips away each time I come close to getting it under the camera. To add to the fun, my camera can’t see it. I take a whole series of photos of nothing. The perfect transparency of the animal means I can only focus on the seaweed below.

The Beroe cucumis comb jelly has a characteristic sack shape.

When another comb jelly washes into the pool, I’m sure there will be lots more opportunities to attempt photos. Stepping out into the open water, I take some time to accustom my eyes, staring past the surface reflection into the water. Soon, I notice comb jellies everywhere.

The irridescent combs of Beroe cucumis

There are dozens, hundreds even, and some are large enough to fill the palm of my hand. Even the large jellies pose a challenge to my camera, but amongst the many seaweed shots, I start to take a few that show off the jellies’ light display.

While most are the large species, Beroe cucumis, with their characteristic sack shape, there are a few smaller ones amongst them. These are sea gooseberries, Pleurobrachia pileus. They are barely a couple of centimetres long, spherical, with two trailing tentacles.

A sea gooseberry with trailing tentacles. Its combs are arranged in lines up its sides.

Despite their tiny size, they are just as mesmerising as the B. Cucumis, the lines down their sides flickering every colour of the rainbow.

Sparkles of irridescence from a passing Sea gooseberry

Among all the comb jellies I spot an even smaller interloper, a hydroid medusa. Hydroids are related to jellyfish, but their adult form usually lives attached to seaweeds, stones or shells. This minute creature is a baby hydroid, looking very much like a jellyfish as it actively swims past, beating its bell fringed with short tentacles.

Hydroid medusa – probably Clytia hemisphaerica swimming by

The pattern of the cross on top of it and the fringe of dark spots around the edge of the bell suggest that it is a young Clytia hemispherica.

Hydroid medusa showing its delicate pattern and short tentacles.

The glare of sunlight on my screen combined with the transparency of all the animals I’m trying to photograph make it impossible to tell how I am doing. I give up taking photos and simply enjoy the spectacle until the tide calls time and forces me back up the beach.

Comb jellies are supposed to phosphoresce, which would be amazing to see. I’m wondering if I can sneak in a little night time rockpooling this weekend. Although the jellies are here in huge numbers today, they may disappear as quickly as they arrived. I should be working, but some things are just too exciting.

The sun shone, which is always a good start, and I couldn’t have asked for a more enthusiastic group. After the morning’s presentation and a lot of work on topshell identification, we enjoyed a perfect picnic on Gyllingvase beach, taking care to protect our sandwiches from the herring gulls, before setting out to explore the rocks.

I was showing some of the group the different topshells, winkles and other shells found near the top of the shore, when someone found a coil of eggs under a stone. It was a perfect start – the eggs of a great grey sea slug (Aeolidia filomenae). We looked all around the area and couldn’t see the slug that had laid them, but it was probably still close by.

Great grey sea slug eggs – from another day because I didn’t take a photo of ones we saw at Falmouth.

Inspired by our early success, we carried on down the shore and one of the group found some codium seaweed. Remembering that I’d mentioned that the photosynthesising sea slug, Elysia viridis, is often found on this seaweed, she called me over.

The lump on the codium she’d hoped might be a slug was seaweed, but we examined the codium some more and soon found two photosynthesising slugs on it. The shout of, ‘Slug’, went up so that everyone could gather to take a look.

Elysia viridis, the photosynthesising sea slug. This slug retains the chloroplasts from the seaweeds it eats and they carry on producing energy inside its body.

Gyllingvase has all sorts of seaweeds, lots of pools and steep rocky overhangs, which makes it a perfect habitat for snails. We found the egg capsules of the netted dog whelk and the European sting winkle among many other things.

‘Slug!’ The shout went up again, this time for a big brown sea hare (Aplysia punctata) and before long we’d seen several of them. They love the sea lettuce and other seaweeds that are growing rapidly in the pools this time of year. They were congregating all over the beach to lay their pink spaghetti egg strings on the seaweed.

Sea hare, Aplysia punctata

We had another shout, that turned out to be this beautiful candy-striped flatworm. It’s not a mollusc of course, but was still a great find.

Candy-striped flatworm at Gyllingvase, Falmouth

It was clear there were plenty of creatures to be found and the entire group took the search seriously, crawling on the rocks, staring into pools, lifting seaweed and bringing all sorts of finds to me.

In a kelp-strewn gully at the edge of the sea, we found more snail eggs of various sorts and some live sting winkles. A sea lemon was sheltering in a small hole in the rock, our fourth sea slug species of the day.

The sea lemon, showing its feathery gills (top) and the rhinophores on its head (bottom).

We put it in a pot of water to watch its rhinophores emerge from its head and its gill feathers unfurl on its back.

By now the tide was starting to turn, so I placed the sea lemon back on its rock and hurried to take a look down another promising gully. There were some anemones about, the favourite food of the great grey sea slug whose eggs we’d seen at the beginning, so I hoped I might find one hanging about there somewhere.

After a few minutes of examining an overhang and taking a look under stones I’d drawn a blank and stopped to take a look at some finds people had brought to me. I was about to haul myself back up the rocks when I spotted a long stone that was half-wedged against the rounded overhang at the back of the pool. It looked like a sluggy sort of stone, one that wouldn’t move easily and might have all sorts of sponges, squirts and other things slugs like to eat growing on or near it.

As soon as I turned the stone, I could see the colourful cerrata of a little slug. It most definitely wasn’t a great grey sea slug with its bright reds and blues. I screamed, ‘Slug!’ loudly enough for most of Falmouth to hear and fumbled with a petri dish, scared I might drop the slug in the water and lose it.

Facelina auriculata sea slug

The great thing about teaching a workshop is that everyone there is just as excited by marine creatures as me, and this one, a Facelina auriculata, is one of the most beautiful slugs I’ve seen on the shore. It caused a lot of excitement and photo taking.

Facelina auriculata sea slug

After returning the Facelina auriculata, which we nicknamed ‘the patriotic slug’ due to its red, white and blue colours, I turned my attention to a deep pool to look at some rainbow wrack. Lovely though the turquoise iridescence of rainbow wrack is, it wasn’t the seaweed itself that interested me, but the colony of various hydroids growing on it. These colonial animals are relatives of the jellyfish and anemones and are a favourite food of many sea slugs.

I was hoping to find a Eubranchus farrani, a colourful slug with fat cerrata and orange markings on its body, which loves to eat hydroids. I soon spotted a tiny slug, but it was something different. It was so small I could barely see it, but in the petri dish when it came out fully I could see under my camera’s magnification that it was a Polycera quadrilineata, a pretty white slug with yellow markings and yellow-tipped tentacles.

Polycera quadrilineata sea slug at Gyllingvase, Falmouth

It was hard to see much with the naked eye, but we all had hand lenses and cameras to get a close look.

Polycera quadrilineata sea slug, Gyllingvase, Falmouth

By this time the tide was rushing in. A last foray along a higher gully produced a cowrie shell and a perfectly orange common starfish, which isn’t a mollusc but made us happy nonetheless.

By the end of the day we’d seen five species of sea slug, the egg spiral of the great grey sea slug and all sorts of snails. It was the kind of fantastic result that comes from lots of dedicated people searching and a good dose of luck.

I can only hope that my run of workshop luck holds for my jellyfish course later in the year. Who knows what might turn up?

Nights out tend to become a distant memory when you’re a parent. For the most part I don’t miss them. I have, however, been looking forward to Junior being old enough to join me for night time rock pooling. Towards the end of last year, we tried it for the first time and, although the conditions weren’t ideal, he’s been asking to go again ever since.

The best low tides always happen around the middle of the day, and the middle of the night, but we compromise for this first family expedition of the year, choosing a reasonable low tide at around 10.30pm. The warm, calm weather provides good opportunities for seeing nocturnal activity and tonight I’m trying out my ultraviolet (UV) torch.

It doesn’t disappoint.

Head torch at the ready – night time rock pooling is a perfect adventure

I’ve always known that certain species glow under UV light, but I had no idea how much. We’ve barely taken ten paces out across the rocks when we see our first snakelocks anemone, shining from the darkness like an eerie green beacon. The colour is wonderfully alien.

Snakelocks anemone at night under UV light – a true alien of the Cornish rock pools

This fluorescence is caused by certain proteins within the animals that take in light of one colour and emit it as another. Some deeper water species can use these properties to appear red, even though red light is filtered out as it passes through the water, meaning the only light available to underwater creatures is UV or blue.

It’s not clear why snakelocks anemones and other sea creatures might want to fluoresce in this way. It seems there may be some benefit in it for their symbiotic algae or it might give them sun protection. It may just be a by-product of a protein that’s useful in other ways. Whatever the reasons, it produces an incredible glow. Junior is already talking of coming back at Halloween.

A spooky night-time rock pooling walk is definitely on the programme for this Halloweeen!

It’s not just the anemones that take our breath away. If you’re used to rock pooling in daylight when most animals are hiding away under rocks and seaweed, the sheer level of activity in after dark takes you by surprise.

A scratching, crackling sound stops us in our tracks. It’s coming from the rocks. I lift the seaweed to show Junior a group of limpets. Some are feeding, their strong radulas scouring seaweed off the rock and chipping bits of rock. Others are setting into their home scars, grinding their shells into their grooves to create a perfect fit. Close-up, their activities make a surprising amount of noise.

Limpets on their way home as the tide retreats

Most rockpool animals are largely nocturnal. Pools that seem empty in daytime become bustling cities of activity. We watch hermit crabs milling around in large numbers, crabs marauding through the pool and across the rocks, fish floating in plain sight. Prawns come towards the light and watch us before shooting away backwards.

A green shore crab looking blue in the UV lightHermit crabs are more active at night, every pool is teeming with them

Other Half spots a small species of spider crab (Macropodia sp.) decorated with long fronds of seaweed edging sideways across the pool. It’s moving too fast to take a clear photo in the poor light. The blurring makes it look even more alien.

A blurry small spider crab (Macropodia sp) moving across sand.

A scorpion fish lies still on the sand, watching out for prey.

A scorpion fish (Taurus bubalis) hiding in plain sight.

One surprise is the stunning colours of the seaweeds under the UV light. Some of the dark red seaweeds take on a far more intense, bright colour, glowing red, pink and orange. Where the top shells have worn spires, their tips glow pink.

A grey topshell on a red seaweed under UV light

After an hour, tiredness and cold begin to set in. We switch off our torches and take a moment to gaze at the stars before we head home to bed. Junior is already asking if we can come again the next night, and the next.